PREVALENCE OF THREE-ROOTED PRIMARY MANDIBULAR FIRST AND SECOND MOLARS USING VERTICAL BITE-WING RADIOGRAPH

* Introduction and objectives * Methods * Results * Conclusions

* Knowledge of root canal anatomy is important for dental practice and for identifying features of anthropological significance. Three-rooted permanent mandibular first molars are common occurrences in the Mongoloid race. * This study aimed to determine the prevalence of three- rooted primary mandibular first and second molars in Taiwanese subjects.

* Prevalence of Three-rooted Mandibular First Molars amongst Taiwanese Individuals (J Endodontics, 2007) --The prevalence of three-rooted mandibular first molars was 21.09%. The bilateral incidence of a symmetrical distribution was % * Detection of Permanent Three-Rooted Mandibular First Molars by Cone-Beam CT Imaging in Taiwanese Individuals (J Endodontics, 2009) --The prevalence of permanent three-rooted mandibular first molars was 33.33%, with a bilateral incidence of a symmetrical distribution of 53.65%. * Prevalence of three-rooted primary mandibular first molars in Taiwan (J Formosa Medical Association, 2009) --The data presented here indicate that approximately 5% of Taiwanese subjects had a three rooted mandibular primary first molar and 80% of such teeth occurred unilaterally. * Prevalence of 3-Rooted Primary Mandibular Second Molars among Chinese Patients (J Pediatric Dentistry, 2010) --Eighteen (9%) 3-rooted primary mandibular second molars were found in the 185 patients, with a bilateral incidence of a symmetrical distribution of 28% (5/18).

* Vertical bite-wing radiographs of 113 subjects (226 teeth), which had been obtained previously in the Department of Pediatric Dentistry, Taichung Veterans General Hospital, Taiwan were screened retrospectively.

* Images of 113 subjects [51 boys and 62 girls; mean age (range), 5.8 (2.4–10.4) years] who had bilateral primary mandibular first and second molars were studied. * The sex, symmetry and frequency of occurrence of three- rooted primary mandibular first and second molars were recorded and statistically analyzed.

Distribution of three-rooted molars in both side 1st and 2nd primary molars (113 subjects).

* The prevalence of subjects with left side three-rooted primary mandibular molars was 1.77% (2/113) in the firsts, 3.54% (4/113) in the seconds, and 0.88% (1/113) in both. * The prevalence of subjects with right side three-rooted primary mandibular molars was 3.54% (4/113) in the firsts, 3.54% (4/113) in the seconds, and 0% (0/113) in both. Neither Only 1 st primary molar Only 2 nd primary molar Both teethp-value† Left Male5147 (92.16)1 (1.96)2 (3.92)1 (1.96) Female6259 (95.16)1 (1.61)2 (3.23)0 (0.00) Total (93.81)2 (1.77)4 (3.54)1 (0.88) Right Male5149 (96.08)1 (1.96) 0 (0.00) Female6256 (90.32)3 (4.84) 0 (0.00) Total (92.92)4 (3.54) 0 (0.00) *Data presented as n (%); † Fisher’s exact test

* Such prevalence did not differ significantly between the right and left sides of the mandible, bilateral and unilateral, or with sex. * The occurrence of teeth that showed an extra root in two primary mandibular molars according unilateral or bilateral side showed girls are higher than boys but did not differ significantly.

Approximately 4.4% of Taiwanese subjects had a three-rooted mandibular primary second molar in the left side, but if the same objects who already have three- rooted mandibular primary first molar, the occurrence rate to have three-rooted mandibular primary second molar is 33.3%.

Figure 1. Three-rooted primary mandibular 1st molars illustrated by vertical bite-wing radiographs. (A) The distolingual root occurred on the left side unilaterally, (B) the distolingual root occurred on the right side unilaterally, (C-D) bilateral symmetrical occurrence of three-rooted mandibular 1st molar teeth in the same patient.

Figure 3. Two cases of both 1st and 2nd primary mandibular molars featured with three-roots (arrows). Figure 2. A clinical case of a 9 years old boy revealed a three-rooted primary 1st molar which has been extracted.

* The prevalence of subjects with left side three-rooted primary mandibular molars was 1.77% (2/113) in the firsts, 3.54% (4/113) in the seconds, and 0.88% (1/113) in both. * The prevalence of subjects with right side three-rooted primary mandibular molars was 3.54% (4/113) in the firsts, 3.54% (4/113) in the seconds, and 0% (0/113) in both. * Such prevalence did not differ significantly between the right and left sides of the mandible, bilateral and unilateral, or with sex. * The occurrence of teeth that showed an extra root in two primary mandibular molars according unilateral or bilateral side showed girls are higher than boys but did not differ significantly. * Dentists should take into account the prevalence of these three-rooted variants in primary mandibular first and second molars among Taiwanese patients during their daily endodontic and exodontic procedures.